Thermal recording material for offset printing

ABSTRACT

Provided is a thermal recording material having excellent offset printability, having a support, a thermal recording layer and a protective layer containing a pigment and a resin, the thermal recording layer being formed on the support, the protective layer being formed on the thermal recording layer, wherein the transfer amount of water on the surface of said protective layer for a contact time period of 150 ms, measured by a Bristow method, is 3 ml/m 2  to 15 ml/m 2  and the contact angle between the surface of said protective layer and water is 60° to 100°.

TECHNICAL FIELD

The present invention relates to a thermal recording material, morespecifically to a thermal recording material having a protective layerthat is excellent in offset printability and at the same time exhibitssuitable surface strength and color developability in thermal printing.

TECHNICAL BACKGROUND

Generally, a thermal recording material has a substrate and aheat-sensitive recording layer formed thereon, the heat-sensitiverecording layer containing, as main components, a colorless orlight-colored electron-donating dye precursor and an electron-acceptingcompound (developer). When the thermal recording material is heated witha thermal head, a hot pen or a laser beam, the dye precursor and thedeveloper readily react with each other to give a recorded image. Suchthermal recording materials give recordings with a relatively simpleapparatus and have advantages that their maintenance is easy and thatthey make no noise. They are used in broad fields of measuringrecorders, facsimile machines, printers, computer terminals, labels,automatic vending machines of railway tickets, and the like.

In recent years, particularly, thermal recording materials have come tobe used as accounting-related recording sheets such as various receipts,CD/ATM slips of banking facilities, receipts of gas, water andelectricity issued with a handy terminal, and the like. Thermalrecording materials for use therefor are required to satisfy thefollowing; the amount of residues adhering to the thermal head of athermal printer should be small, so that no printing failure is to takeplace in long-distance printing even without carrying out anymaintenance/checkout such as the cleaning of the thermal head. Thesoiling of a developed color due to an external pressure, scratching,etc., should not take place (resistance to rubbing-induced fogging), anda recorded surface should not be peeled off even if it is wetted withrainwater (water resistance) (for example, see JP-A-2-169291). For thepurpose of decreasing the deposit of residues on a thermal head andimproving a thermal recording material in resistance to rubbing-inducedfogging and water resistance, generally, there is well known a method inwhich a protective layer is formed on a thermal recording layer (forexample, see JP-A-9-263049, JP-A-10-147059 and JP-A-5-294067).

In the above thermal recording materials for use as accounting-relatedrecording sheets, it is mostly required to apply offset printing, andthere are increasingly demanded thermal recording materials excellent inthe lithographic offset printability using a dampening solution. Whenthe above protective layer is formed, however, the protective layer ismostly formed from a resin, so that it has picking resistance, while itis said that the protective layer is unsuitable for offset printingsince the protective layer is poor in the property of taking ink and theproperty of properly absorbing water. As a method of improving theoffset printability of a thermal recording material having a protectivelayer, there is known a method in which binders for an undercoat layerand a protective layer are specified, and there is known a recordingmaterial having a specific relationship between a contact angle to waterand a contact angle to linseed oil, while they are not sufficient (forexample, see JP-A-7-149048 and JP-A-4-82777).

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a thermal recordingmaterial comprising a support, a thermal recording layer formed thereonand a protective layer formed on the thermal recording layer, whichthermal recording material is excellent in offset printability and atthe same is excellent in surface strength and thermal printability. Forachieving the above object, the present inventors have made diligentstudies and as a result have found that the above object can be achievedwhen the transfer amount of water on the protective layer surface andthe contact angle between the surface of the protective layer and waterare in predetermined ranges. The present invention has been accordinglycompleted.

That is, the present invention is directed to;

-   -   (1) a thermal recording material for offset printing, comprising        a support, a thermal recording layer for thermally developing a        color and a protective layer containing a pigment and a resin,        the thermal recording layer being formed on the support, the        protective layer being formed on the thermal recording layer,        wherein the transfer amount of water on the surface of said        protective layer for a contact time period of 150 ms, measured        by a Bristow method, is 3 ml/m² to 15 ml/m² and the contact        angle between the surface of said protective layer and water is        60° to 100°,    -   (2) the thermal recording material for offset printing as        recited in the above (1), wherein the transfer amount of water        on the surface of said protective layer for a contact time        period of 150 ms, measured by a Bristow method, is 7 ml/m² to 10        ml/m²,    -   (3) the thermal recording material for offset printing as        recited in the above (1), wherein the contact angle between the        surface of said protective layer and water is 70° to 90°,    -   (4) the thermal recording material for offset printing as        recited in the above (1), wherein the surface of said protective        layer has a center plane average roughness (SRa), measured with        a stylus type three-dimensional surface roughness tester, of 0.6        μm to 2 μm in a coating direction at a cutoff value of 0.8 mm,    -   (5) the thermal recording material for offset printing as        recited in the above (1), wherein the surface of said protective        layer has a center plane average roughness (SRa), measured with        a stylus type three-dimensional surface roughness tester, of 0.6        μm to 1 μm in a coating direction at a cutoff value of 0.8 mm,    -   (6) the thermal recording material for offset printing as        recited in the above (1), wherein the pigment contained in the        said protective layer has an oil absorption, measured according        to JIS-K-5101, of 200 ml/100 g to 350 ml/100 g,    -   (7) the thermal recording material for offset printing as        recited in the above (1), wherein the pigment contained in the        said protective layer has an oil absorption, measured according        to JIS-K-5101, of 250 ml/100 g to 300 ml/100 g,    -   (8) the thermal recording material for offset printing as        recited in any one of the above (1), (2), (4) and (6), wherein        the resin in said protective layer is at least one member of a        water-dispersible resin and a non-modified polyvinyl alcohol and        said protective layer has a pigment content of 40 mass % to 70        mass % based on the total solid content of said protective        layer,    -   (9) the thermal recording material for offset printing as        recited in the above (1), wherein the transfer amount of water        on the surface of said protective layer for a contact time        period of 150 ms, measured by a Bristow method, is 7 ml/m² to 10        ml/m², the contact angle between the surface of said protective        layer and water is 70° to 90°, the surface of said protective        layer has a center plane average roughness (SRa), measured with        a stylus type three-dimensional surface roughness tester, of 0.7        μm to 2.0 μm in a coating direction at a cutoff value of 0.8 mm,        the resin in said protective layer is at least one member of a        water-dispersible resin and a non-modified polyvinyl alcohol,        the pigment has an oil absorption, measured according to        JIS-K-5101, of 250 ml/100 g to 300 ml/100 g and said protective        layer has a pigment content of 40 mass % to 70 mass % based on        the total solid content of said protective layer,    -   (10) the thermal recording material for offset printing as        recited in the above (1), wherein the resin in said protective        layer is a silicon-modified polyvinyl alcohol and the protective        layer contains a high-molecular-weight crosslinking agent and a        low-molecular-weight crosslinking agent,    -   (11) the thermal recording material for offset printing as        recited in the above (10), wherein said high-molecular-weight        crosslinking agent contains a glycidyl group and contains        polyamideamine as a main chain,    -   (12) the thermal recording material for offset printing as        recited in the above (10), wherein said low-molecular-weight        crosslinking agent is a compound having an aldehyde group,    -   (13) the thermal recording material for offset printing as        recited in the above (10), wherein said high-molecular-weight        crosslinking agent contains a glycidyl group and contains        polyamideamine as a main chain, and said low-molecular-weight        crosslinking agent is a compound having an aldehyde group,    -   (14) the thermal recording material for offset printing as        recited in the above (13), wherein said high-molecular-weight        crosslinking agent is contained in an amount of 2 mass % to 10        mass % based on the solid content of the resin in said        protective layer and said low-molecular-weight crosslinking        agent is contained in an amount of 2 mass % to 8 mass % based on        the solid content of the resin in said protective layer,    -   (15) the thermal recording material for offset printing as        recited in the above (10), wherein the surface of said        protective layer has a center plane average roughness (SRa),        measured with a stylus type three-dimensional surface roughness        tester, of 0.6 μm to 2 μm in a coating direction at a cutoff        value of 0.8 mm,    -   (16) the thermal recording material for offset printing as        recited in the above (10), wherein said protective layer has a        pigment content of 10 mass % to 50 mass % based on the total        solid content of said protective layer, and    -   (17) the thermal recording material for offset printing as        recited in the above (13), wherein the transfer amount of water        on the surface of said protective layer for a contact time        period of 150 ms, measured by a Bristow method, is 3 ml/m² to 10        ml/m², the contact angle between the surface of said protective        layer and water is 70° to 90°, the surface of said protective        layer has a center plane average roughness (SRa), measured with        a stylus type three-dimensional surface roughness tester, of 0.6        μm to 2 μm in a coating direction at a cutoff value of 0.8 mm,        and said protective layer has a pigment content of 10 mass % to        50 mass % based on the total solid content of said protective        layer.

PREFERRED EMBODIMENTS OF THE INVENTION

The thermal recording material of the present invention is a material inwhich a thermal recording layer for thermally developing a color and aprotective layer containing a resin and a pigment are consecutivelyformed on a support. In the thermal recording material, the transferamount of water on the surface of the above protective layer for acontact time period of 150 ms, measured by a Bristow method (J. TAPPIpaper pulp testing method No. 51-87; to be simply referred to as“Bristow method” hereinafter), is 3 ml/m² to 15 ml/m², and the contactangle between the surface of the above protective layer and water is 60°to 100°.

First, the numerical requirements of the protective layer of the thermalrecording material of the present invention will be explained. As amethod of evaluating the permeability of water to paper, etc.,conventionally, there are used a Stockigt sizing degree test and a Cobbsizing degree test in addition to the Bristow method in the presentinvention.

The Bristow method is a method in which a liquid is transferred from ahead box having a slit in a lower portion to a test piece on a rotatingwheel, and it is an evaluation method using a relationship that thetransfer amount of a liquid per unit area after the liquid contacts apaper is in proportion to a square root of a time. As compared with theabove Stockigt sizing degree test and the above Cobb sizing degree test,the Bristow method is a method in which the momentary water absorptioncharacteristic of a coating layer surface for one second or less can beaccurately grasped, and the thus-obtained data can be an effective indexfor knowing the permeation behavior of a dampening solution in actualoffset printing.

In the thermal recording material of the present invention, the transferamount of water on the surface of the protective layer for a contacttime period of 150 ms, measured by the Bristow method, is limited to 3ml/m² to 15 ml/m². When the transfer amount of water on the protectivelayer is less than 3 ml/m², a dampening solution remaining on theprotective layer surface decreases the property of taking ink in offsetprinting. When the transfer amount of water on the protective layersurface exceeds 15 ml/m², the permeation of a dampening solution maydecrease the coating layer strength. The transfer amount of water ispreferably 7 ml/m² to 10 ml/m².

Further, the contact angle in the present invention refers to a contactangle (°) measured 1 second after a distilled water droplet is droppedon the protective layer surface in an atmosphere of 23° C. and 50% RH.In the present invention, it is required to obtain an accurate data ofthe wettability of the protective layer surface to water, and themeasurement of the contact angle can be an effective index for knowingthe behavior of a dampening solution transferred to the protective layersurface in actual offset printing, in addition to the momentary waterabsorption characteristic of the protective layer surface for 1 secondor less, obtained by the above Bristow method. For the measurement of acontact angle in the present invention, there can be used, for example,a FACE automatic contact angle meter supplied by KYOWA INTERFACE SCIENCECO., LTD.

In the present invention, the contact angle of water on the protectivelayer surface is limited to 60° to 100°. When the contact angle of wateris less than 60°, the replacement of water with ink is impeded, and theadherence of ink is degraded, so that a density non-uniformity or adensity decrease in an image portion are liable to take place. Further,when it exceeds 100°, a non-image portion is liable to be soiled. Thecontact angle of water is preferably 70° to 90°.

Further, the center plane average roughness (SRa) of the aboveprotective layer surface, measured with a stylus type three-dimensionalsurface roughness tester in a coating direction at a cutoff value of 0.8mm, is preferably 0.6 μm to 2 μm, more preferably 0.6 μm to 1 μm. Whenthe above ranges are satisfied, there can be obtained a thermalrecording material excellent in ink absorptivity, a printed imagequality and thermally printed character quality.

The center plane average roughness (SRa) measured with a stylus typethree-dimensional surface roughness tester in a coating direction at acutoff value of 0.8 mm refers to a roughness defined by the followingexpression 1. $\begin{matrix}{{SRa} = {\frac{1}{Sa}{\int_{0}^{W_{x}}{\int_{0}^{W_{y}}{{{f\left( {x,y} \right)}}{\mathbb{d}x}{\mathbb{d}y}}}}}} & \left\lbrack {{Equation}\quad 1} \right\rbrack\end{matrix}$

In the expression 1, W_(x) is a length of a sample surface region in theX-axis direction (coating direction), W_(y) is a length of the samplesurface region in the y-axis direction (direction perpendicular to thecoating direction), and Sa is an area of the sample surface region.Further, f(x,y) is a function showing a roughness of the sample surfaceon the xy plane.

Specifically, the center plane average roughness (SRa) can bedetermined, for example, by using a machine model SE-3AK supplied byKosaka Laboratory Ltd. as a stylus type three-dimensional surfaceroughness tester and a machine model SPA-11 supplied by KosakaLaboratory Ltd. as an analyzer at a cutoff value of 0.8 mm underconditions of Wx=20 mm and Wy=8 mm, that is, under the condition ofSa=160 mm². In this case, 500 points are sampled for data processing inthe X-axis direction and scanning of 17 lines or more in the Y-axisdirection is carried out.

The water absorption characteristic according to the Bristow method, thecontact angle property and the center plane average roughness (SRa) canbe adjusted depending upon kinds and amount ratios of materials forconstituting the protective layer, coating methods, finish methods, andthe like.

The method of improving the water absorption characteristic according tothe Bristow method includes, for example, methods of using a hydrophilicresin such as polyvinyl alcohol, using a pigment excellent in moistureabsorption property, using a larger amount of a pigment component andadjusting a coating method or a finish method to increase the roughnessof a thermal paper and other method. The method of increasing thecontact angle includes methods of using a hydrophobic resin, using apigment of which the surface is treated to be hydrophobic, decreasingthe amount of a pigment component, adding a crosslinking agent toimprove a resin in film formability, adding a hydrophobic material suchas WAX and adjusting a coating method or a finish method to smoothen thesurface and other method. Since, however, carrying out these methodsdecreases the water absorption characteristic, it is important tooptimize both the water absorption characteristic and the contact angleproperty, and in the present invention, the water absorptioncharacteristic and the contact angle property are optimized by adjustingthem by combining these methods, so that the thermal recording materialis improved in offset printability.

The method of adjusting the center plane average roughness (SRa)includes methods of adding a crosslinking agent or adjusting heating toadjust the film formability of a resin, adjusting the particle diameter,kind and amount of a pigment, adjusting a coating method, adjusting afinish method such as calendering, and other method.

In the thermal recording material of the present invention, theprotective layer contains a resin and a pigment. The resin that iscontained in the protective layer is not specially limited, and theresin is properly selected as required in a relationship to the pigmentto be described later, such that the water absorption characteristic onthe protective layer according to the Bristow method, the contact angleto water and the center plane average roughness (SRa) come into thespecified ranges, while it is preferred to use a water-soluble resin ora water-dispersible resin. The water-soluble resin or thewater-dispersible resin can be selected from known water-soluble resinsor water-dispersible resins as required. The water-soluble resin is notspecially limited. For example, as a polyvinyl alcohol, modifiedalcohols such as an acetoacetylated modified polyvinyl alcohol, asilicon-modified polyvinyl alcohol, etc., and a non-modified polyvinylalcohol can be used. Further, the water-soluble resin can be selectedfrom starch or a derivative thereof, cellulose derivatives such ashydroxyethyl cellulose, methyl cellulose, ethyl cellulose andcarboxymethyl cellulose, polyvinyl pyrrolidone, polyacrylamide, anacrylamide/acrylate copolymer, an acrylamide/acrylate/methacrylateterpolymer, an alkali salt of polyacrylic acid, an alkali salt ofpolymaleic acid, an alkali salt of a styrene/maleic anhydride copolymer,an alkali salt of an ethylene/maleic anhydride copolymer, an alkali saltof an isobutylene/maleic anhydride copolymer, sodium alginate, gelatin,casein, an acid neutralization product of chitosan, or the like.Preferably, non-modified polyvinyl alcohol or silicon-modified polyvinylalcohol can be used.

The non-modified polyvinyl alcohol in the present invention refers to aproduct that is obtained by hydrolyzing or saponifying polyvinylacetate, or the like to a proper degree and that is not subjected tomodification treatment such as acetoacetylation modification. Thesilicon-modified polyvinyl alcohol refers to a polyvinyl alcoholcontaining silicon in the molecule thereof, and it includes a silylatedpolyvinyl alcohol and a product obtained by copolymerizing vinyl esterand a silicon-containing olefin monomer and then saponifying theresultant copolymer.

Although not specially limited, examples of the water-dispersible resininclude a styrene/butadiene copolymer, an acrylonitrile/butadienecopolymer, a methyl acrylate/butadiene copolymer, anacrylonitrile/butadiene/styrene terpolymer, a polyvinyl acetate, a vinylacetate/acrylate copolymer, an ethylene/vinyl acetate copolymer,polyacrylic ester, a styrene/acrylate copolymer, polyurethane and acore-shell acrylic emulsion. Preferably, core-shell type acrylicemulsions such as “Barrier Star” supplied by Mitsui Chemicals Inc. areincluded.

The above water-soluble resins or water-dispersible resins may be usedsingly or as a mixture containing at least two members of these.

Although not specially limited, examples of the pigment that iscontained in the protective layer include inorganic pigments such asdiatomite, talc, kaolin, calcined kaolin, calcium carbonates includingheavy calcium carbonate and precipitated calcium carbonate, magnesiumcarbonate, zinc oxide, aluminum oxide, aluminum hydroxide, magnesiumhydroxide, titanium dioxide, barium sulfate, zinc sulfate, amorphoussilica, amorphous calcium silicate and colloidal silica, and organicpigments such as a melamine resin filler, a urea-formalin resin filler,a polyethylene powder and a nylon powder. Preferably, amorphous silicaand calcium carbonate are included. These pigments may be used singly ormay be used as a mixture containing at least two members of them asrequired.

Although not specially limited, the average particle diameter of thepigment for use in the protective layer is preferably 2 μm or less forincreasing an image density.

As a pigment, a pigment having an oil absorption amount, measuredaccording to JIS-K-5101, of 200 ml/100 g to 350 ml/100 g is preferred,and a pigment having such an oil absorption amount of 250 ml/100 g to300 ml/100 g is more preferred. Since a pigment having the above oilabsorption is used, there can be obtained a thermal recording materialthat is well-balanced between the water absorption characteristic of thesurface of protective layer and the adherence of ink thereto.

When at least one of the water-dispersible resin and the non-modifiedpolyvinyl alcohol is used as a resin, preferably, the protective layercontains the pigment in an amount of 40 mass % to 70 mass % based on thetotal solid content of the protective layer. When the silicon-modifiedpolyvinyl alcohol is used as a resin for the above protective layer, itis preferred to use the pigment in an amount of 10 mass % to 50 mass %based on the solid content of the protective layer. Since the abovecompositions are employed, there can be attained a well balance betweenthe excellent water absorption characteristic and the adherence of ink.

The water absorption characteristic of the protective layer can beadjusted by incorporating a crosslinking agent to the protective layeras required. The crosslinking agent for use in the protective layerincludes a low-molecular-weight crosslinking agent and ahigh-molecular-weight crosslinking agent. The low-molecular-weightcrosslinking agent includes low-molecular-weight compounds having amolecular weight of 300 or less, such as compounds having an aldehydegroup (formalin, etc.), aziridine, dimethylolurea and guanamine.Compounds having an aldehyde group are preferred.

The high-molecular-weight crosslinking agent includes polymer compoundshaving a molecular weight of greater than 300, such as dialdehydestarch, epoxy resins, higher carboxylic acids, an N-methylolmelamineresin and a compound containing a glycidyl group and having a main chainformed of a polyamideamine. Preferred is a compound containing aglycidyl group and having a main chain formed of a polyamideamine. Whenthe protective layer contains a high-molecular-weight crosslinkingagent, the thermal recording material is improved in layer strength dueto a crosslinking effect and is improved in offset printability. When acompound containing a glycidyl group and having a main chain formed of apolyamideamine is used, the thermal recording material can be moreimproved in offset printability.

The content of the high-molecular-weight crosslinking agent in theprotective layer based on the solid content of the resin is 2 mass % to20 mass %, preferably 2 mass % to 10 mass %, more preferably 2 mass % to5 mass %. Further, the content of the low-molecular-weight crosslinkingagent in the protective layer based on the solid content of the resin ispreferably 2 mass % to 8 mass %.

When the low-molecular-weight crosslinking agent is used together withthe high-molecular-weight crosslinking agent, the effect of protectingthe recording surface can be more improved as is the primary object ofthe protective layer, the necessary coating amount for the protectivelayer can be decreased, and there can be obtained thermal recordingmaterial having high thermal color developing properties, which are allpreferred. In this case, preferably, a compound having a glycidyl groupand containing a polyamideamine as a main chain is used as ahigh-molecular-weight crosslinking agent, and a compound having analdehyde group is used as a low-molecular-weight crosslinking agent.Concerning the contents of these, preferably, the content of thehigh-molecular-weight crosslinking agent based on the solid content ofthe resin in the protective layer is 2 mass % to 10 mass %, and thecontent of the low-molecular-weight crosslinking agent based on thesolid content of the resin in the protective layer is 2 mass % to 8 mass%.

In the thermal recording material having the protective layer using asilicon-modified polyvinyl alcohol as a resin and containing thehigh-molecular-weight crosslinking agent and the low-molecular-weightcrosslinking agent, 10 mass % to 50 mass %, based on the total solidcontent of the protective layer, of a pigment is incorporated into theprotective layer, whereby there can be obtained a thermal recordingmaterial that is well-balanced between the water absorptioncharacteristic of the surface thereof and the adherence of ink thereto.

The protective layer may contain other additives for preventing thewearing of a head and the sticking, and such other additives includehigher fatty acid metal salts such as zinc stearate and calciumstearate, waxes such as paraffin, paraffin oxide, polyethylene,polyethylene oxide, stearic acid amide and castor wax, dispersing agentssuch as sodium dioctylsulfosuccinate, a surfactant and a fluorescencedye.

The solid coating amount for the protective layer is 0.2 to 10 g/m²,preferably 0.5 to 5 g/m². The protective layer may have a multilayerstructure formed of two or more layers as required. When the solidcoating amount is within the above range, coloring caused on a ground bya frictional heat from scratching or rubbing, which is called“rubbing-induced fogging”, can be prevented and suitable thermalresponse can be obtained.

The thermal recording layer constituting the thermal recording materialof the present invention will be explained. The thermal recording layeris obtained by dispersing a generally colorless or light-coloredelectron-donating dye precursor and an electron-accepting developer asmain components in a binder and coating the thus-obtained coating liquidon a support. The thermal recording layer is locally heated in use,whereby the precursor and the electron-accepting compound readily reactwith each other to give a recorded image.

Although not specially limited, the dye precursor for use in the thermalrecording layer can be selected from those which are generally used inthermal recording materials or pressure-sensitive recording materials.The dye precursor includes, for example, triarylmethane compounds,diphenylmethane compounds, xanthene compounds, thiazine compound andspiro compounds.

(1) Examples of the triarylmethane compounds include3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (Crystal VioletLactone), 3,3-bis(p-dimethylaminophenyl) phthalide,3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl) phthalide,3-(p-dimethylaminophenyl)-3-(2-methylindol-3-yl) phthalide,3-(p-dimethylaminophenyl)-3-(2-phenylindol-3-yl) phthalide,3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide,3,3-bis(1,2-dimethylindol-3-yl)-6-dimethylaminophthalide,3,3-bis(9-ethylcarbazol-3-yl)-5-dimethylaminophthalide,3,3-bis(2-phenylindol-3-yl)-5-dimethylaminophthalide and3-p-dimethylaminophenyl-3-(1-methylpyrol-2-yl)-6-dimethylaminophthalide.

(2) Examples of the diphenylmethane compounds include4,4′-bis(dimethylaminophenyl)benzhydrylbenzyl ether,N-chlorophenylleucoauramine and N-2,4,5-trichlorophenylluecoauramine.

(3) Examples of the xanthene compounds include rhodamine Banilinolactam, rhodamine B-p-chloroanilinolactam,3-diethylamino-7-benzylamino-fluorane,3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane,3-diethylamino-7-chlorofluorane,3-diethylamino-6-chloro-7-methylfluorane,3-diethylamino-7-(3,4-dichloroanilino)fluorane,3-diethylamino-7-(2-chloroanilino)fluorane,3-diethylamino-6-methyl-7-anilinofluorane,3-dibutylamino-6-methyl-7-anilinofluorane,3-dipentylamino-6-methyl-7-anilinofluorane,3-(N-ethyl-N-tolyl)amino-6-methyl-7-anilinofluorane,3-piperidino-6-methyl-7-anilinofluorane,3-(N-ethyl-N-tolyl)amino-6-methyl-7-phenethylfluorane,3-diethylamino-7-(4-nitroanilino)fluorane,3-dibutylamino-6-methyl-7-anilinofluorane,3-(N-methyl-N-propyl)amino-6-methyl-7-anilinofluorane,3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluorane,3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluorane, and3-(N-ethyl-N-tetrahydrofurfuryl)amino-6-methyl-7-anilinofluorane.

(4) Examples of the thiazine compounds include Benzoylluecomethyleneblue and p-nitrobenzoylleucomethylene blue.

(5) Examples of the spiro compounds include 3-methylspironaphthopyran,3-ethylspirodinaphthopyran, 3,3′-dichlorospirodinaphthopyran,3-benzylspirodinaphthopyran, 3-methylnaphtho-(3-methoxybenzo)spiropyranand 3-propylspirobenzopyran.

These dye precursors may be used singly or may be used as a mixturecontaining at least two members of them as required.

Although not specially limited, the electron-accepting compound for usein the thermal recording material can be selected from those acidicsubstances which are generally used in thermal recording materials orpressure-sensitive recording materials. For example, theelectron-accepting compound can be selected from clay substances, phenolderivatives, aromatic carboxylic acid derivatives, urea derivatives suchas N,N′-diallylthiourea derivatives and N-sulfonylurea, or metal saltsof these.

Specific examples of the above compound include clay substances such asactivated clay, zeolite and bentonite, phenolic compounds such as4-phenylphenol, 4-tert-butylphenol, 4-hydroxyacetophenone,2,2′-dihydroxydiphenyl, 2,2′-methylenebis(4-methyl-6-tert-butylphenol),4,4′-ethylenebis(2-methylphenol), 1,1-bis(4-hydroxyphenyl)propane,1,1-bis(4-hydoxyphenyl)-pentane, 1,1-bis(4-hydroxyphenyl)hexane,1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxyphenyl)propane,2,2-bis(4-hydroxyphenyl)hexane, 2,2-bis(4-hydroxyphenyl)-3-ethylhexane,2,2-bis(3-chloro-4-hydroxyphenyl)-propane,1,1-bis(4-hydroxyphenyl)-1-phenylethane,1,1-bis(4-hydroxyphenyl)-1-phenylpropane, 4,4′-dihydroxydiphenyl ether,4,4′-cyclohexylidenebis(2-isopropylphenol),4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone,4-hydroxy-4′-methyldiphenylsulfone,4-hydroxy-4′-isopropoxydiphenylsulfone,4-hydroxy-4′-n-propoxydiphenylsulfone,4-hydroxy-4′-benzyloxydiphenylsulfone,bis(3-allyl-4-hydroxyphenyl)sulfone,bis(3-chloro-4-hydroxyphenyl)sulfone, 2,4-bis(phenylsulfonyl)-phenol,bis(3-chloro-4-hydroxyphenyl)sulfide,4,4′-thiobis(2-tert-butyl-5-methylphenol),2,2′-bis(4-hydroxyphenylthio)diethyl ether,1,7-di(4-hydroxyphenylthio)-3,5-dioxaheptane, dimethyl4-hydroxypthalate, 2,2-bis(4-hydroxyphenyl)acetic esters, alkyl gallicesters, salicylanilide, 5-chlorosalicylanilide, a novolak type phenolicresin and a modified terpene phenolic resin, hydroxybenzoic esters suchas ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, butyl4-hydroxybenzoate, benzyl 4-hydroxybenzoate and chlorobenzyl4-hydroxybenzoate, organic acids such as benzoic acid, salicylic acid,1-hydroxy-2-naphthoic acid, 2-hydroxy-6-naphthoic acid,3-isopropylsalicylic acid, 3-cyclohexylsalicylic acid,5-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid,3,5-di-tert-nonylsalicylic acid, 3,5-didodecylsalicylic acid,3-methyl-5-tert-dodecylsalicylic acid,3,5-bis(α,α-dimethylbenzyl)salicylic acid,3-methyl-5-(α-methylbenzyl)salicylic acid,4-n-octyloxycarbonyl-aminosalicylic acid,4-{2-(4-methoxyphenoxy)-ethoxy}salicylic acid, tartaric acid, oxalicacid, boric acid, citric acid and stearic acid, metal salts of thesesuch as zinc, nickel, aluminum or calcium salts of these, ureaderivatives such asbis{4-(4-methylphenyl)-sulfonylaminocarbonylaminophenyl}methane, andknown compounds such as thiourea derivatives. These compounds may beused singly or may be used as a mixture containing two or more membersof them as required.

The thermal recording layer constituting the thermal recording materialof the present invention may contain a heat-fusible compound forimproving the thermal response thereof. Although the heat-fusiblecompound is not specially limited, it preferably has a melting point of60° C. to 180° C., particularly preferably 80° C. to 140° C.

Specific examples of the above heat-fusible compound include fatty acidamides such as stearic acid amide, N-hydroxymethylstearic acid amide,N-stearylstearic acid amide, ethylenebisstearic acid amide, oleic acidamide, palmitic acid amide, methylenebis hydrogenated tallow fatty acidamide and ricinoleic acid amide, synthetic and natural waxes such asparaffin wax, microcrystalline wax, polyethylene wax and carnauba wax,aliphatic urea compounds such as N-stearylurea, ether compounds such as2-benzyloxynaphthalene, bis(4-methoxyphenyl)ether,2,2′-bis(4-methoxyphenoxy) diethyl ether,1,2-bis(3-methylphenoxy)ethane, 1,2-bis(phenoxymethyl)benzene, anaphthyl ether derivative, an anthryl ether derivative and an aliphaticether, ester compounds such as diphenyl adipate,di(4-methylbenzyl)oxalate, dibenzyl oxalate, di(4-chlorobenzyl)oxalate,diphenyl carbonate, dimethyl terephthalate, dibenzyl terephthalate,phenyl benzenesulfonate and 4-acetylacetophenone, biphenyl derivativessuch as m-terphenyl, 4-benzylbiphenyl, 4-acetylbiphenyl,4-allyloxybiphenyl, and known heat-fusible compounds such asbis(4-allyloxyphenyl)sulfone, acetoacetic acid anilide,4-methylacetoanilide and fatty acid anilides. These heat-fusiblecompounds may be used singly or may be used as a mixture containing twoor more members of them as required.

The amount of the heat-fusible compound by mass ratio is in the range of0.3 to 2 times as large as the above electron-accepting compound, morepreferably in the range of 0.5 to 1.5 times as large. When it is in theabove range, there can be obtained a thermal recording materialexcellent in basic properties such as thermal response, saturationdensity of a color-developed image, whiteness of a ground, and the like.

In addition, as a pigment in the thermal recording layer, there may beused inorganic pigments such as diatomite, talc, kaolin, calcinedkaolin, heavy calcium carbonate, precipitated calcium carbonate,magnesium carbonate, zinc oxide, aluminum oxide, aluminum hydroxide,magnesium hydroxide, titanium dioxide, barium sulfate, zinc sulfate,amorphous silica, amorphous calcium silicate and colloidal silica, andorganic pigments such as a melamine resin filler, a urea-formalin resinfiller, a polyethylene powder and a nylon powder.

As other additives to the thermal recording layer, for preventing thewearing of a hot printing head or preventing the sticking, there may beused higher fatty acid metal salts such as zinc stearate and calciumstearate, waxes such as paraffin, paraffin oxide, polyethylene,polyethylene oxide, stearic acid amide and castor wax, dispersing agentssuch as sodium dioctylsulfosuccinate, ultraviolet absorbents such asbenzophenone- and benzotriazole-containing ultraviolet absorbents, asurfactant and a fluorescence dye as required.

For the thermal recording layer for constituting the thermal recordingmaterial of the present invention, various water-soluble resins orwater-dispersible resins may be used as a binder.

Although not specially limited, examples of the abovehigh-molecular-weight resins include starches, cellulose derivativessuch as hydroxymethylcellulose, methylcellulose, ethylcellulose andcarboxymethylcellulose, proteins such as gelatin and casein,water-soluble binders such as polyvinyl alcohol, modified polyvinylalcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, anacrylamide/acrylic ester copolymer, an acrylamide/acrylicester/methacrylic acid terpolymer, an alkali salt of polyacrylic acid,an alkali salt of polymaleic acid, an alkali salt of a styrene/maleicacid anhydride copolymer, an alkali salt of an ethylene/maleic acidanhydride copolymer and an alkali salt of an isobutylene/maleic acidanhydride copolymer, and water-dispersible binders such as astyrene/butadiene copolymer, an acrylonitrile/butadiene copolymer, amethyl acrylate/butadiene copolymer, an acrylonitrile/butadiene/styreneterpolymer, polyvinyl acetate, a vinyl acetate/acrylic ester copolymer,an ethylene/vinyl acetate copolymer, polyacrylic ester, astyrene/acrylic ester copolymer and polyurethane. These binders may beused singly or may be used as a mixture containing at least two membersof them as required.

The color-developing components such as the dye precursor, theelectron-accepting compound, etc., and the additives such as theheat-fusible compound, the pigment, the binder, etc., which are to becontained in the thermal recording layer, are applied to a support inthe form of a dispersion of them in a dispersing medium, and dried. Theabove dispersion is obtained by a method in which the color-developingcomponents and the other additive components are dry-milled anddispersed in a dispersing medium or a method in which thecolor-developing components and the other additive components are mixedwith a dispersing agent and wet-milled.

The average particle diameter of those compounds which constitute thecolor-developing components in the above dispersion is generally 7 μm orless, preferably 0.05 to 5 μm, more preferably 0.1 to 2 μm. When it isin the above range, there can be obtained a thermal recording materialexcellent in the transparency and color developability of the thermalrecording layer.

The coating amount of the thermal recording layer as a solid coatingamount of the dye precursor is generally 0.1 to 2 g/m², more preferably0.15 to 1.5 g/m². When it is in the above range, sufficientcolor-development sensitivity can be obtained without any disadvantagein economic performance.

The thermal recording material of the present invention may be providedwith at least one undercoat layer formed of one or more pigments and abinder between the support and the thermal recording layer as required.When the thermal recording material of the present invention is providedwith the undercoat layer, the coating amount of the undercoat layer ispreferably 1 to 30 g/m², more preferably 3 to 20 g/m².

Although not specially limited, the pigment for the undercoat layer canbe selected from inorganic pigments such as calcined kaolin, diatomite,talc, kaolin, heavy calcium carbonate, precipitated calcium carbonate,magnesium carbonate, zinc oxide, aluminum oxide, aluminum hydroxide,magnesium hydroxide, titanium dioxide, barium sulfate, zinc sulfate,amorphous silica, amorphous calcium silicate and colloidal silica, andorganic pigments such as a melamine resin filler, a urea-formalin resinfiller, a polyethylene powder and a nylon powder. Organic sphericalparticles and organic hollow particles can be also used. Calcined kaolinis preferred.

The binder for the undercoat layer can be selected from variouswater-soluble and water-dispersible resins. Specific examples thereofinclude those binders which are described as specific examples of thebinder for use in the above thermal recording layer. The binders may beused singly or may be used as a mixture containing at least two membersof them.

In the present invention, paper is mainly used as the support. Besidesthe paper, the support can be selected from various woven fabrics,non-woven fabrics, synthetic resin films, synthetic resin laminatedpapers, synthetic papers, metal foils, vapor-deposited sheets orcomposite sheets combining these by laminating, as required.

The thermal recording material of the present invention can be obtainedby forming the undercoat layer on the support as required and thenconsecutively forming the thermal recording layer and the protectivelayer.

The method of forming the protective layer, the thermal recording layeror the undercoat layer is not specially limited, and these layers can beformed according to conventionally known techniques. As a specificexample, the coating liquid is applied by a method such as air knifecoating, rod blade coating, bar coating, blade coating, gravure coating,curtain coating, or E bar coating, and the applied coating liquid isdried to form the protective layer, the thermal recording layer or theundercoat layer.

Further, each of the thermal recording layer, the protective layer,etc., can be formed by various printing machines according to a methodof lithography, letterpress, flexography, gravure, screen or hot melt.

Further, after the application to form the undercoat layer, after theapplication to form the thermal recording layer or after the applicationto form the protective layer, super calendering may be carried out toimprove image qualities.

While the thermal recording material of the present invention is appliedto offset printing, it can be applied particularly to lithographicoffset printing in which printing is carried out using a dampeningsolution and utilizing a repulsion between water and an oil (ink).

The present invention will be explained with reference to Exampleshereinafter, while the present invention shall not be limited by theseExamples. In the following Examples and Comparative Examples,evaluations were made for a transfer amount of water by the Bristowmethod, contact angles, center plane average roughness (SRa), offsetprintability, surface strength and thermal printing color developabilityby the following methods. In samples used in Examples and ComparativeExamples, “%” and “part” are all based on mass standard, and applicationamounts stand for absolute dry application amounts.

[Measurement for Transfer Amount of Water by Bristow Method]

In an atmosphere of 23° C. and 50% RH, a measurement was made for atransfer amount of water on a protective layer for a contact time periodof 150 ms using a head box having a 0.5 mm wide slit, to which a 30 μlof a 0.1% kayafect red B (direct dye supplied by NIPPON KAYAKU CO.,LTD.) aqueous solution was injected, with a Bristow tester supplied byToyo Seiki Seisaku-sho, Ltd.

[Measurement of Contact Angle]

A distilled water droplet was dropped on a protective layer surface, andafter 1 second, the water droplet was measured for a contact angle witha FACE automatic contact angle meter CA-Z model supplied by KYOWAINTERFACE SCIENCE CO., LTD.

[Measurement of Center Plane Average Roughness (SRa)]

Determined with an SE-3AK model machine and an SPA-11 model machinesupplied by Kosaka Laboratory Ltd., as a stylus type three-dimensionalsurface roughness tester, at a cutoff value of 0.8 mm with Wx=20 mm andWy=8 mm, i.e., under the conditions of Sa=160 mm². In the dataprocessing in the X-axis direction, sampling was made in 500 points, andscanning of 17 lines or more in the Y-axis direction was carried out(unit: μm).

[Offset Printability]

A thermal recording material was evaluated for offset printability withan RI testing machine supplied by Akira Seisakusho Co., Ltd. The surfaceof a thermal recording material was thinly wetted with water, andprinting was carried out using 0.4 cc of Trans G Indigo Normal (suppliedby Dainippon Ink & Chemicals, Inc.) as ink. A state where the inkadhered thereto was visually evaluated. The visual valuation of theink-adhering state was made on the basis of the following ratings.

1. The ink adherence is very good, and a thermal recording material hasexcellent offset printability.

2. The ink adherence is good, and a thermal recording material has goodoffset printability.

3. The ink adherence is good, and a thermal recording material has nopractical problem in offset printing.

4. The ink adherence is poor, and a thermal recording material has apractical problem in offset printing.

5. Almost no ink adheres, and a thermal recording material ispractically not feasible for offset printing.

[Surface Strength]

A thermal recording material was evaluated for surface strength with anRI testing machine supplied by Akira Seisakusho Co., Ltd. Printing wasmade on the surface of a thermal recording material several times with atackiness No. 10 blank ink, and the printed surface was visuallyevaluated for a picking (peeling of the thermal recording materialsurface). The visual valuation was made on the basis of the followingratings.

1. Almost no peeling is found.

2. Peeling is found to a slight extent, but there is no problem inpractical use.

3. Peeling is found to some extent, but there is no problem in practicaluse.

4. Peeling is found to a great extent, and there is a problem inpractical use.

5. Peeling is found to a very great extent, and a thermal recordingmaterial is not acceptable in practical use.

[Color Developability in Thermal Printing]

A printing test was carried out with a facsimile tester TH-PMD suppliedby Okura Electric Co., Ltd. A thermal head having a dot density of 8dots/mm and a head resistance of 1,681 Ω was used, and printing wascarried out by electrically powering at a head voltage of 21 V at apulse width of 1.4 msec. A printing was measured for an optical densitywith a Macbeth RD-918 reflection densitometer. The larger the value is,the superior in color developability in thermal printing, and theoptical density is preferably at least 0.7 in practical use.

<Preparation of Dispersion for Thermal Recording Layer and Dispersionfor Protective Layer>

Dispersions A, B, C and D for thermal recording layers and Dispersions1, 2 and 3 for protective layers used in Examples and ComparativeExamples were prepared by the following methods.

(Dispersion for Thermal Recording Layer)

(Dispersion A)

200 Grams of 3-(N,N-dibutylamino)-6-methyl-7-anilinofluorane as a dyeprecursor was dispersed in a mixture of 200 g of a 10% polyvinyl alcoholaqueous solution with 600 g of water, and the dispersion was milled witha bead mill until an average particle diameter of 1 μm was attained, togive Dispersion A.

(Dispersion B)

400 Grams of 2,2-bis(4-hydroxyphenyl)-propane as an electron-acceptingcompound was dispersed in a mixture of 400 g of a 10% polyvinyl alcoholaqueous solution with 200 g of water, and the dispersion was milled witha bead mill until an average particle diameter of 1 μm was attained, togive Dispersion B.

(Dispersion C)

400 Grams of 2-benzyloxynaphthalene as a heat-fusible compound wasdispersed in a mixture of 400 g of a 10% polyvinyl alcohol aqueoussolution with 200 g of water, and the dispersion was milled with a beadmill until an average particle diameter of 1 μm was attained, to giveDispersion C.

(Dispersion D)

200 Grams of calcium carbonate (Brilliant 15, supplied by ShiraishiKogyo K.K.) as a pigment was mixed with 800 g of a 0.5% sodiumpolyacrylate aqueous solution and dispersed therein with a homomixer for10 minutes, to give Dispersion D.

(Preparation of Dispersion for Protective Layer)

(Dispersion 1) 100 Grams of amorphous silica (Mizukasil P-707, suppliedby Mizusawa Industrial Chemicals, Ltd.) having an oil absorption,measured according to JIS-K-5101, of 260 ml/100 g was mixed with 900 gof a 0.5% sodium polyacrylate aqueous solution and dispersed thereinwith a homomixer for 10 minutes, to give Dispersion 1.

(Dispersion 2)

200 Grams of calcium carbonate (Callite, supplied by Shiraishi KogyoK.K.) having an oil absorption, measured according to JIS-K-5101, of 90ml/100 g was mixed with 800 g of a 0.5% sodium polyacrylate aqueoussolution and dispersed therein with a homomixer for 10 minutes, to giveDispersion 2.

(Dispersion 3)

Grams of amorphous silica (Mizukasil P-603, supplied by MizusawaIndustrial Chemicals, Ltd.) having an oil absorption, measured accordingto JIS-K-5101, of 115 ml/100 g was mixed with 900 g of a 0.5% sodiumpolyacrylate aqueous solution and dispersed therein with a homomixer for10 minutes, to give Dispersion 3.

EXAMPLE 1

(A) Preparation of Thermal Coating Paper

A wood-free paper having a basis weight of 40 g/m² was provided as asupport, and an under sheet layer coating liquid having the followingformulation was air-knife coated thereon so as to attain a solid coatingamount of 9 g/m² and dried, to prepare a thermal coating paper. Calcinedkaolin (Ansilex supplied by 100 parts Engelhard Corporation) 50%Styrene-butadiene latex aqueous  24 parts dispersion Water 200 parts(B) Preparation of Thermal Recording Layer Coating Liquid

Dispersions A to D were used, and these and materials were mixed inamounts shown below, and the mixture was fully stirred to prepare athermal recording layer coating liquid. Dispersion A 20 parts DispersionB 15 parts Dispersion C 15 parts Dispersion D 25 parts 10% Polyvinylalcohol (Aqueous solution of 30 parts GM-14L supplied by NipponSynthetic Chemical Industry Co., Ltd.) aqueous solution Water 30 parts(C) Preparation of Protective Layer Coating Liquid

A water-dispersible core-shell type acrylic emulsion having a solidcontent of 20% and having a core that was formed of acrylonitrile as anessential component and had a glass transition temperature (Tg) of −12°C. and a shell that was formed of acrylamide as an essential componentand had a glass transition temperature (Tg) of 205° C. (this will bereferred to as “20% core-shell type acrylic emulsion (Z)” hereinafter)and materials were mixed in amounts shown below, and the mixture wasfully stirred to prepare a protective layer coating liquid. Table 1 alsoshows the composition of the protective layer. 20% Core-shell typeacrylic emulsion (Z)  50 parts Dispersion 1 150 parts 40% Zinc stearateaqueous solution  6 parts Water 250 parts(Preparation of Thermal Recording Material)

The thermal recording layer coating liquid prepared in (B) was air-knifecoated on the thermal coating paper prepared in (A) so as to obtain adye precursor coating amount of 0.3 g/m², and the thus-coated coatingliquid was dried. Then, the protective layer coating liquid prepared in(C) was air-knife coated on the thermal recording layer so as to obtaina coating amount of 5 g/m², and the thus-coated coating liquid wasdried, followed by super calendering, to give a thermal recordingmaterial.

The thermal recording material obtained by the above method was measuredfor a transfer amount of water according to the Bristow method, acontact angle with the water, a center plane average roughness (SRa) andoffset printability. Table 2 shows the results.

EXAMPLE 2

A thermal recording material was obtained in the same manner as inExample 1 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 2 shows evaluation results of theobtained thermal recording material. 20% Core-shell type acrylicemulsion (Z)  25 parts Dispersion 2  75 parts 40% Zinc stearate aqueoussolution  6 parts Water 270 parts

EXAMPLE 3

A thermal recording material was obtained in the same manner as inExample 1 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 2 shows evaluation results of theobtained thermal recording material. 20% Core-shell type acrylicemulsion (Z)  25 parts 10% Completely saponified polyvinyl  50 partsalcohol (aqueous solution of NL-05 supplied by Nippon Synthetic ChemicalIndustry Co., Ltd.) Dispersion 2  50 parts 40% Zinc stearate aqueoussolution  6 parts Water 240 parts

COMPARATIVE EXAMPLE 1

A thermal recording material was obtained in the same manner as inExample 1 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 2 shows evaluation results of theobtained thermal recording material. 15% Polyacrylamide resin (HARICOATBI-736,  67 parts supplied by Harima Chemicals, Inc.) Dispersion 2  25parts 40% Zinc stearate aqueous solution  6 parts Water 190 parts

COMPARATIVE EXAMPLE 2

A thermal recording material was obtained in the same manner as inExample 1 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 2 shows evaluation results of theobtained thermal recording material. 20% Core-shell type acrylicemulsion (Z)  25 parts 10% Completely saponified polyvinyl  50 partsalcohol (aqueous solution of NL-05 supplied by Nippon Synthetic ChemicalIndustry Co., Ltd.) Dispersion 2  25 parts 40% Zinc stearate aqueoussolution  6 parts Water 185 parts

COMPARATIVE EXAMPLE 3

A thermal recording material was obtained in the same manner as inExample 1 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 2 shows evaluation results of theobtained thermal recording material. 20% Core-shell type acrylicemulsion (Z)  50 parts Dispersion 1  50 parts 40% Zinc stearate aqueoussolution  6 parts Water 185 parts

COMPARATIVE EXAMPLE 4

A thermal recording material was obtained in the same manner as inExample 1 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 2 shows evaluation results of theobtained thermal recording material. 15% Polyacrylamide resin (HARICOATBI-736,  67 parts supplied by Harima Chemicals, Inc.) Dispersion 1  10parts 40% Zinc stearate aqueous solution  6 parts Water 210 parts

TABLE 1 Composition of protective layer (part) Water Sticking dis- pers-ible Water-soluble preventing resin Water-soluble resin resin + pigmentCrosslinking agent liquid Other High- High- 20% 10% mol- mol- Low- CoreCom- 10% ecular- ecular- mol- Low- shell pletely Silicon- weight weightecular- ecular- Disper- type saponi- 15% modi- type type weight weightsion acrylic fied Pol- fied Dis- Dis- Dis- (poly- (modi- type type of40% emul- poly- acryla- poly- per- per- per- amide fied (alde- (guana-zinc sion vinyl mide vinyl sion sion sion amine- amine hyde minestearate Coating (Z) alcohol resin alcohol 1 2 3 based) based) group)group in water Water amount Example 1 50 150 6 250 5 g/m² Example 2 2575 6 270 ↑ Example 3 25 50 50 6 240 ↑ Compara- 67 25 6 190 ↑ tiveExample 1 Compara- 25 50 25 6 185 ↑ tive Example 2 Compara- 50 50 6 185↑ tive Example 3 Compara- 67 10 6 210 ↑ tive Example 4 Example 4 thesame components as those in Example 1 2 g/m² Example 5 the samecomponents as those in Example 2 ↑ Example 6 the same components asthose in Example 3 ↑ Example 7 100 150 6 200 ↑ Compara- the samecomponents as those in Comparative Example 2 ↑ tive Example 5 Compara-the same components as those in Comparative Example 2 ↑ tive Example 6Compara- the same components as those in Comparative Example 2 ↑ tiveExample 7 Compara- the same components as those in Comparative Example 2↑ tive Example 8 Compara- 50 10 6 157 ↑ tive Example 9 Compara- 50 350 6384 ↑ tive Example 10 Compara- 25 200 1 12.5 224 0.5 g/m² tive Example11 Compara- 50 400 400 25 791 2 g/m² tive Example 12

TABLE 2 Transfer amount of Center water plane according average Oil torough- absorp- Bristow Contact ness tion of Offset method angle (SRa)pigment print- (ml/m²) (° C.) (μm) (ml/100 g) ability Ex. 1 8.4 72.20.72 260 1 Ex. 2 7.1 62.3 0.61 90 2 Ex. 3 9.1 75.6 0.58 90 3 CEx. 1 2.847.6 0.51 90 5 CEx. 2 2.8 58.9 0.61 90 4 CEx. 3 2.4 54.3 0.66 260 4 CEx.4 2.0 45.0 0.49 260 5

As is clear from Tables 1 and 2, when Examples 1 to 3 and ComparativeExamples 1 to 4 are compared, it is seen that a thermal recordingmaterial having a thermal recording layer and a protective layer formedconsecutively is improved in offset printability by adjusting thetransfer amount of water on the protective layer surface for a contacttime of 150 ms according to the Bristow method to 3 ml/m²-15 ml/m² andadjusting the contact angle of the protective layer surface and water to60°-100°.

Further, when Examples 1 and 2 and Example 3 are compared, it is seenthat the thermal recording material is improved in offset printabilityby adjusting the center plane average roughness (SRa) in a coatingdirection at a cutoff value of 0.8 mm, measured with a stylus typethree-dimensional surface roughness tester, to 0.6 μm-2 μm. Further,when Examples 1 and 2 are compared, it is seen that there is produced aneffect that the thermal recording material is more improved in offsetprintability by incorporating a pigment component having an oilabsorption, measured according to JIS-K-5101, of 200 ml/100 g -350ml/100 g into the protective layer.

EXAMPLE 4

A thermal recording material was obtained in the same manner as inExample 1 except that the protective layer coating liquid prepared in(C) of Example 1 was air-knife coated on the thermal recording layer soas to obtain a coating amount of 2 g/m² followed by drying and supercalendering.

Table 1 shows the composition of the protective layer coating liquid,and Table 3 shows evaluation results. In this Example and Examples andComparative Examples thereafter, thermal recording materials wereevaluated for surface strength and color developability in thermalprinting in addition to the evaluations thereof for transfer amounts ofwater according to the Bristow method, contact angles, center planeaverage roughness, oil absorptions of pigments and offset printability.

EXAMPLE 5

A thermal recording material was obtained in the same manner as inExample 4 except that the formulation in Example 2 was used as aprotective layer coating liquid. Table 1 shows the composition of theprotective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material.

EXAMPLE 6

A thermal recording material was obtained in the same manner as inExample 4 except that the formulation in Example 3 was used as aprotective layer coating liquid. Table 1 shows the composition of theprotective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material.

EXAMPLE 7

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of thethermal recording material. 10% Completely saponified polyvinyl 100parts alcohol (aqueous solution of NL-05 supplied by Nippon SyntheticChemical Industry Co., Ltd.) Dispersion 1 150 parts 40% Zinc stearateaqueous solution  6 parts Water 200 parts

COMPARATIVE EXAMPLE 5

A thermal recording material was obtained in the same manner as inExample 4 except that the formulation in Comparative Example 1 was usedas a protective layer coating liquid. Table 1 shows the composition ofthe protective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material.

COMPARATIVE EXAMPLE 6

A thermal recording material was obtained in the same manner as inExample 4 except that the formulation in Comparative Example 2 was usedas a protective layer coating liquid. Table 1 shows the composition ofthe protective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material.

COMPARATIVE EXAMPLE 7

A thermal recording material was obtained in the same manner as inExample 4 except that the formulation in Comparative Example 3 was usedas a protective layer coating liquid. Table 1 shows the composition ofthe protective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material.

COMPARATIVE EXAMPLE 8

A thermal recording material was obtained in the same manner as inExample 4 except that the formulation in Comparative Example 4 was usedas a protective layer coating liquid. Table 1 shows the composition ofthe protective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material.

COMPARATIVE EXAMPLE 9

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 20% Core-shell type acrylicemulsion (Z)  50 parts Dispersion 1  10 parts 40% Zinc stearate aqueoussolution  6 parts Water 157 parts

COMPARATIVE EXAMPLE 10

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 20% Core-shell type acrylicemulsion (Z)  50 parts Dispersion 1 350 parts 40% Zinc stearate aqueoussolution  6 parts Water 384 parts

COMPARATIVE EXAMPLE 11

A thermal recording material was obtained in the same manner as inExample 1 except that the following formulation was used as a protectivelayer coating liquid and that the thus-prepared protective layer coatingliquid was air-knife coated on the thermal recording layer so as toobtain a coating amount of 0.5 g/m² followed by drying and supercalendering. Table 1 shows the composition of the protective layercoating liquid, and Table 3 shows the evaluation results of the obtainedthermal recording material. 10% Completely saponified polyvinyl 25 partsalcohol (aqueous solution of NL-5 supplied by Nippon Synthetic ChemicalIndustry Co., Ltd.) Dispersion 1 200 parts High-molecular-weightcrosslinking agent 1 part containing polyamideamine as a main chain(25%) (WS-547, supplied by Nippon PMC Co., Ltd.) 40% Zinc stearateaqueous solution 12.5 parts Water 224 parts

COMPARATIVE EXAMPLE 12

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Completely saponified polyvinyl400 parts alcohol 20% Core-shell type acrylic emulsion (Z)  50 partsDispersion 3 400 parts 40% Zinc stearate aqueous solution  25 partsWater 791 parts

As is clear from Tables 1 and 3, when Examples 4 to 7 and ComparativeExamples 5 to 12 are compared, it is seen that excellent offsetprintability and suitable surface strength can be obtained in a thermalrecording material having a thermal recording layer and a protectivelayer formed consecutively by adjusting the transfer amount of water onthe protective layer surface for a contact time of 150 ms according tothe Bristow method to 3 ml/m²-15 ml/m² and adjusting the contact angleof the protective layer surface and water to 60°-100®.

Further, when Examples 5 and 6 are compared, it is seen that the thermalrecording material is improved in offset printability by adjusting thecenter plane average roughness (SRa) in a coating direction at a cutoffvalue of 0.8 mm, measured with a stylus type three-dimensional surfaceroughness tester, to 0.6 μm or more. Further, when Examples 4 and 5 arecompared, it is seen that the thermal recording material is moreimproved in offset printability by incorporating a pigment componenthaving an oil absorption, measured according to JIS-K-5101, of 200ml/100 g or more into the protective layer.

Example 7 is a case where the water-dispersible resin in Example 4 wasreplaced by the completely saponified polyvinyl alcohol, and the thermalrecording material in Example 7 exhibited nearly similar properties.When evaluated visually closely, the thermal recording material inExample 4 was superior in offset printability and surface strength tosome extent.

EXAMPLE 8

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 2 25 parts 40% Zinc stearate aqueous solution 6 partsHigh-molecular-weight crosslinking agent 4 parts having a glycidyl groupcontaining polyamideamine as a main chain (25%) (WS-547, supplied byNippon PMC Co., Ltd.) Low-molecular-weight crosslinking agent 2 partshaving an aldehyde group (40%) (glyoxal) Water 210 parts

EXAMPLE 9

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 2 25 parts 40% Zinc stearate aqueous solution 6 partsHigh-molecular-weight crosslinking agent 2 parts having a glycidyl groupand containing polyamideamine as a main chain (25%) (WS-547, supplied byNippon PMC Co., Ltd.) Low-molecular-weight crosslinking agent 2 partshaving an aldehyde group (40%) (glyoxal) Water 210 parts

EXAMPLE 10

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 1 50 parts 40% Zinc stearate aqueous solution 6 partsHigh-molecular-weight crosslinking agent 2 parts having a glycidyl groupand containing polyamideamine as a main chain (25%) (WS-547, supplied byNippon PMC Co., Ltd.) Low-molecular-weight crosslinking agent 2 partshaving an aldehyde group (40%) (glyoxal) Water 185 parts

EXAMPLE 11

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 2 25 parts 40% Zinc stearate aqueous solution 6 partsHigh-molecular-weight crosslinking agent 2.2 parts containing a modifiedamine resin as a main component (45%) (Sumirez Resin SPI-102A, suppliedby Sumitomo Chemical Co., Ltd.) Low-molecular-weight crosslinking agent2 parts having an aldehyde group (40%) (glyoxal) Water 218 parts

EXAMPLE 12

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 1 50 parts 40% Zinc stearate aqueous solution 6 partsHigh-molecular-weight crosslinking agent 2 parts having a glycidyl groupand containing polyamideamine as a main chain (25%) (WS-547, supplied byNippon PMC Co., Ltd.) Low-molecular-weight crosslinking agent 0.8 parthaving a guanamine group (100%) (Acetoguanamine) Water 189 parts

EXAMPLE 13

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 1 50 parts 40% Zinc stearate aqueous solution 6 partsHigh-molecular-weight crosslinking agent 10 parts having a glycidylgroup and containing polyamideamine as a main chain (25%) (WS-547,supplied by Nippon PMC Co., Ltd.) Low-molecular-weight crosslinkingagent 2 parts having an aldehyde group (40%) (glyoxal) Water 210 parts

EXAMPLE 14

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 1  50 parts 40% Zinc stearate aqueous solution  6 partsHigh-molecular-weight crosslinking agent  10 parts having a glycidylgroup and containing polyamideamine as a main chain (25%) (WS-547,supplied by Nippon PMC Co., Ltd.) Low-molecular-weight cross linkingagent  5 parts having an aldehyde group (40%) (glyoxal) Water 194 parts

COMPARATIVE EXAMPLE 13

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 2  25 parts 40% Zinc stearate aqueous solution  6 parts Water192 parts

COMPARATIVE EXAMPLE 14

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 2  5 parts 40% Zinc stearate aqueous solution  6 partsHigh-molecular-weight crosslinking agent  2 parts having a glycidylgroup and containing polyamideamine as a main chain (25%) (WS-547,supplied by Nippon PMC Co., Ltd.) Low-molecular-weight cross linkingagent  2 parts having an aldehyde group (40%) (glyoxal) Water 163 parts

COMPARATIVE EXAMPLE 15

A thermal recording material was obtained in the same manner as inExample 4 except that the following formulation was used as a protectivelayer coating liquid. Table 1 shows the composition of the protectivelayer coating liquid, and Table 3 shows the evaluation results of theobtained thermal recording material. 10% Silicon-modified polyvinylalcohol 150 parts (R1130, supplied by Shin-Etsu Chemical Co., Ltd.)Dispersion 2 150 parts 40% Zinc stearate aqueous solution  6 partsHigh-molecular-weight crosslinking agent  2 parts having a glycidylgroup and containing polyamideamine as a main chain (25%) (WS-547,supplied by Nippon PMC Co., Ltd.) Low-molecular-weight cross linkingagent  2 parts having an aldehyde group (40%) (glyoxal) Water 501 parts

EXAMPLE 15

A thermal recording material was obtained in the same manner as inExample 4 except that the coating of the protective layer coating liquidon the thermal recording layer and the drying thereof were not followedby the super calendering. Table 1 shows the composition of theprotective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material.

EXAMPLE 16

A thermal recording material was obtained in the same manner as inExample 8 except that the coating of the protective layer coating liquidon the thermal recording layer and the drying thereof were not followedby the super calendering. Table 1 shows the composition of theprotective layer coating liquid, and Table 3 shows the evaluationresults of the obtained thermal recording material. TABLE 3 Transferamount of Center water plane Color according average Oil develop- torough- absorp- ability Bristow Contact ness tion of Offset in methodangle (SRa) pigment print- thermal (ml/m²) (° C.) (μm) (ml/100 g)ability SS* printing Ex. 4 8.1 71.8 0.72 260 1 3 0.84 Ex. 5 6.8 64.80.62 90 2 3 0.82 Ex. 6 8.4 71.7 0.55 90 3 2 1.02 Ex. 7 9.6 68.0 0.75 2601 3 0.87 CEx. 5 4.8 43 0.42 90 4 5 1.11 CEx. 6 3.1 56.6 0.54 90 4 4 0.98CEx. 7 2.2 61 0.52 260 4 3 0.93 CEx. 8 2.4 50.2 0.42 260 5 5 1.10 CEx. 92.1 75.3 0.33 260 4 3 1.02 CEx. 10 8.2 56.3 0.69 260 2 5 0.54 CEx. 117.5 54.3 0.64 260 1 4 0.65 CEx. 12 5.8 50.9 0.58 115 3 4 1.15 Ex. 8 5.075.0 0.69 90 1 1 1.18 Ex. 9 6.3 70.4 0.66 90 1 1 1.17 Ex. 10 7.6 67.30.66 260 1 1 1.06 Ex. 11 7.8 60.8 0.64 90 2 2 1.16 Ex. 12 6.7 69.3 0.68260 1 1 0.89 Ex. 13 3.2 81.5 0.63 260 1 2 0.96 Ex. 14 7.0 61.7 0.63 2601 2 0.94 CEx. 13 7.1 35.3 0.64 90 5 2 0.98 CEx. 14 6.3 39.2 0.63 90 5 10.89 CEx. 15 8.4 28.9 0.72 90 3 4 0.71 Ex. 15 11.0 63.1 1.28 260 3 20.71 Ex. 16 8.3 64.6 1.46 90 2 1 0.78Ex. = Example, CEx. = Comparative ExampleSS* = Surface strength

As is clear from Tables 1 and 3, when Example 9 and Example 11 arecompared, it is seen that there is produced an effect that the offsetprintability is improved by using, as a resin in the protective layer, asilicon-modified polyvinyl alcohol and also using 2 mass % to 10 mass %,based on the solid content of the resin in the protective layer, of ahigh-molecular-weight crosslinking agent containing a glycidyl group andhaving a polyamideamine as a main chain and 2 mass % to 8 mass %, basedon the solid content of the resin in the protective layer, of alow-molecular-weight crosslinking agent having an aldehyde group.Further, when Example 10 and Example 12 are compared, it is seen thatthe effect on the color developability in thermal printing differsbetween these two Examples even in a case where the offset printabilityand the surface strength are at similar levels.

In Examples 9 and 10, the ink adherence in the evaluation for the offsetprintability is rated at 1. In visual close evaluation, however, the inkadherence in Example 10 using a pigment having a high oil absorption wassuperior.

Further, when Example 9 is compared with Comparative Examples 14 and 15,it is seen that the offset printability is degraded when the surfacecontact angle is smaller than 60 degrees even if the protective layercontains, as a resin, the silicon-modified polyvinyl alcohol and alsocontains the high-molecular-weight crosslinking agent and thelow-molecular-weight crosslinking agent.

Further, when Examples 4 and 15 are compared and when Examples 8 and 16are compared, it is seen that the thermal recording materials having acenter plane average roughness of smaller than 1 μm in Examples 4 and 8have excellent offset printability over the thermal recording materialshaving a center plane average roughness of greater than 1 μm in Examples15 and 16.

EFFECT OF THE INVENTION

As is clear from the foregoing, in a thermal recording material havingthermal recording layer formed on a support and a protective layercontaining a pigment component and a resin, formed on the thermalrecording layer, the transfer amount of water on the protective layersurface for a contact time period of 150 ms according to the Bristowmethod and the contact angle of the protective layer surface and waterare brought into predetermined ranges, and further, the center planeaverage roughness (Sra) in a coating direction at a cutoff value of 0.8mm, measured with a stylus type three-dimensional surface roughnesstester, are brought into predetermined ranges, whereby there can beobtained a thermal recording material having a protective layer, whichis excellent in offset printability and which has suitable surfacestrength and color developability in thermal printing.

Further, when the protective layer contains a pigment component havingan oil absorption, measured according to JIS-K-5101, of 200 ml/100 g to350 ml/100 g, a water-dispersible resin or a non-modified polyvinylalcohol is used as a resin in the protective layer, and 40 mass % to 70mass %, based on the entire solid content of the protective layer, ofthe pigment component is incorporated, whereby there can be furtherobtained superior effects. Further, a silicon-modified polyvinyl alcoholis used as a resin in the above protective layer, the above protectivelayer contains a high-molecular-weight crosslinking agent, preferably, ahigh-molecular-weight crosslinking agent having a glycidyl group andcontaining polyamidemaine as a main chain and a low-molecular-weightcrosslinking agent, preferably, a low-molecular-weight crosslinkingagent having an aldehyde group, these crosslinking agents being used inamounts of 2 mass % to 10 mass % and 2 mass % to 8 mass %, respectively,based on the solid content of the resin, and further, the aboveprotective layer contains a pigment in an amount of 10 mass % to 50 mass% based on the total solid content of the protective layer, wherebythere can be further obtained excellent results.

INDUSTRIAL UTILITY

The thermal recording material of the present invention is excellent inlithographic offset printability and is useful as various recordingpaper sheets.

1. A thermal recording material for offset printing, comprising asupport, a thermal recording layer for thermally developing a color anda protective layer containing a pigment and a resin, the thermalrecording layer being formed on the support, the protective layer beingformed on the thermal recording layer, wherein the transfer amount ofwater on the surface of said protective layer for a contact time periodof 150 ms, measured by a Bristow method, is 3 ml/m² to 15 ml/m² and thecontact angle between the surface of said protective layer and water is60° to 100°.
 2. The thermal recording material for offset printing asrecited in claim 1, wherein the transfer amount of water on the surfaceof said protective layer for a contact time period of 150 ms, measuredby a Bristow method, is 7 ml/m² to 10 ml/m².
 3. The thermal recordingmaterial for offset printing as recited in claim 1, wherein the contactangle between the surface of said protective layer and water is 70° to90°.
 4. The thermal recording material for offset printing as recited inclaim 1, wherein the surface of said protective layer has a center planeaverage roughness (SRa), measured with a stylus type three-dimensionalsurface roughness tester, of 0.6 μm to 2 μm in a coating direction at acutoff value of 0.8 mm.
 5. The thermal recording material for offsetprinting as recited in claim 1, wherein the surface of said protectivelayer has a center plane average roughness (SRa), measured with a stylustype three-dimensional surface roughness tester, of 0.6 μm to 1 μm in acoating direction at a cutoff value of 0.8 mm.
 6. The thermal recordingmaterial for offset printing as recited in claim 1, wherein the pigmentcontained in the said protective layer has an oil absorption, measuredaccording to JIS-K-5101, of 200 ml/100 g to 350 ml/100 g.
 7. The thermalrecording material for offset printing as recited in claim 1, whereinthe pigment contained in the said protective layer has an oilabsorption, measured according to JIS-K-5101, of 250 ml/100 g to 300ml/100 g.
 8. The thermal recording material for offset printing asrecited in claim 1, wherein the resin in said protective layer is atleast one member of a water-dispersible resin and a non-modifiedpolyvinyl alcohol and said protective layer has a pigment content of 40mass % to 70 mass % based on the total solid content of said protectivelayer.
 9. The thermal recording material for offset printing as recitedin claim 1, wherein the transfer amount of water on the surface of saidprotective layer for a contact time period of 150 ms, measured by aBristow method, is 7 ml/m² to 10 ml/m², the contact angle between thesurface of said protective layer and water is 70° to 90°, the surface ofsaid protective layer has a center plane average roughness (SRa),measured with a stylus type three-dimensional surface roughness tester,of 0.7 μm to 2.0 μm in a coating direction at a cutoff value of 0.8 mm,the resin in said protective layer is at least one member of awater-dispersible resin and a non-modified polyvinyl alcohol, thepigment has an oil absorption, measured according to JIS-K-5101, of 250ml/100 g to 300 ml/100 g and said protective layer has a pigment contentof 40 mass % to 70 mass % based on the total solid content of saidprotective layer.
 10. The thermal recording material for offset printingas recited in claim 1, wherein the resin in said protective layer is asilicon-modified polyvinyl alcohol and the protective layer contains ahigh-molecular-weight crosslinking agent and a low-molecular-weightcrosslinking agent.
 11. The thermal recording material for offsetprinting as recited in claim 10, wherein said high-molecular-weightcrosslinking agent contains a glycidyl group and contains polyamideamineas a main chain.
 12. The thermal recording material for offset printingas recited in claim 10, wherein said low-molecular-weight crosslinkingagent is a compound having an aldehyde group.
 13. The thermal recordingmaterial for offset printing as recited in claim 10, wherein saidhigh-molecular-weight crosslinking agent contains a glycidyl group andcontains polyamideamine as a main chain, and said low-molecular-weightcrosslinking agent is a compound having an aldehyde group.
 14. Thethermal recording material for offset printing as recited in claim 13,wherein said high-molecular-weight crosslinking agent is contained in anamount of 2 mass % to 10 mass % based on the solid content of the resinin said protective layer and said low-molecular-weight crosslinkingagent is contained in an amount of 2 mass % to 8 mass % based on thesolid content of the resin in said protective layer.
 15. The thermalrecording material for offset printing as recited in claim 10, whereinthe surface of said protective layer has a center plane averageroughness (SRa), measured with a stylus type three-dimensional surfaceroughness tester, of 0.6 μm to 2 μm in a coating direction at a cutoffvalue of 0.8 mm.
 16. The thermal recording material for offset printingas recited claim 10, wherein said protective layer has a pigment contentof 10 mass % to 50 mass % based on the total solid content of saidprotective layer.
 17. The thermal recording material for offset printingas recited in claim 13, wherein the transfer amount of water on thesurface of said protective layer for a contact time period of 150 ms,measured by a Bristow method, is 3 ml/m² to 10 ml/m², the contact anglebetween the surface of said protective layer and water is 70° to 90°,the surface of said protective layer has a center plane averageroughness (SRa), measured with a stylus type three-dimensional surfaceroughness tester, of 0.6 μm to 2 μm in a coating direction at a cutoffvalue of 0.8 mm, and said protective layer has a pigment content of 10mass % to 50 mass % based on the total solid content of said protectivelayer.